Also known as: Mairon, The Dark Lord, The Necromancer, Lord Of The Rings
Originally a Maia of Aule named Mairon ("the Admirable"), Sauron was seduced by Morgoth's power and became the greatest and most terrible of his servants. Where Morgoth's evil was rooted in nihilistic destruction and the desire to unmake, Sauron's malice was driven by an obsessive need for order, control, and domination. He was the most dangerous of Morgoth's lieutenants precisely because he was capable of patience, subtlety, and long planning.
During the First Age, Sauron served as lord of Angband's werewolves and held the tower of Tol-in-Gaurhoth (formerly Minas Tirith of Finrod) on the Isle of Werewolves. He was defeated there by Luthien and Huan the Hound, who wrested the tower from him. After Morgoth's defeat in the War of Wrath, Sauron briefly repented and considered surrendering to the Valar, but his pride would not allow him to face their judgment, and he fled into hiding.
In the Second Age, Sauron rose again. Disguising himself as Annatar, "Lord of Gifts," he deceived the Elven-smiths of Eregion, particularly Celebrimbor, and taught them the craft of making Rings of Power. In secret, he forged the One Ring in the fires of Mount Doom, pouring into it a great part of his own native power and will to dominate all other ring-bearers. When the Elves perceived his treachery, he waged war upon them and nearly destroyed them, but was driven back by the armies of Numenor. He was taken as a prisoner to Numenor, where through cunning counsel he corrupted King Ar-Pharazon and the Numenoreans, leading to the destruction of their island kingdom by Iluvatar. Sauron's fair bodily form was destroyed in the Downfall, and thereafter he could never again appear as anything other than terrible and dark.
Returning to Mordor, Sauron rebuilt his power and challenged the Last Alliance of Elves and Men. He was defeated by Isildur, who cut the One Ring from his hand, but Isildur's failure to destroy the Ring ensured Sauron's eventual return. Through the Third Age, Sauron slowly regathered his strength, first as the Necromancer of Dol Guldur and then openly in Mordor. His final defeat came when Frodo and Sam brought the Ring to Mount Doom and Gollum's fall into the fire accomplished what no one else could. With the Ring's destruction, Sauron was diminished to a mere spirit of malice, impotent and blown away by the wind, never to take shape again.